A stock-like (not micro) agency is interested in licensing some of my photos. Their contract has the following clause which sounds awfully restrictive:

“…Neither party has any right to cancel this license…”

While their FAQ claims that they will honor a cancellation "unless there are extraneous [sic] circumstances", it appears that they don't have to - and they don't need any reason to reject a cancellation request. Nor is there any procedure for cancellation of the license apart from the obvious one: trained attack lawyers.

Is this standard practice among stock libraries, and is this as crippling as it sounds?

I don't know for sure, but I guess this protects them in case they've sold one of your images and you then want to cancel with the agency. They don't have to go to their customer and retrieve the image.